© 1995-2007 CORNELL Musical Equipment Design & Development 4
Construction and Design
Virtually all modern amplifiers are built using printed circuit boards, which helps to speed up
production and keep down costs. There is, however, one major drawback with printed
circuits - conductor tracks that connect components together often run very close to one
another, creating a small capacitance. The result of this in a guitar amplifier is a substantial
loss in both high frequency response and harmonic richness.
Cornell amplifiers are designed to avoid this by having point-to-point wiring throughout.
Components are mounted onto a specially designed component board which is then
sealed, using a conformal coating to prevent noise and the reduction of component life
caused by moisture penetration.
The hand wiring, carried out by our highly-trained staff, takes time but ensures that each of
our amplifiers performs to the highest standards of reliability and sound.
The stainless steel chassis holds our specially-designed transformers, and chassis-
mounted (rather than circuit-board mounted) valves (tubes).
Such attention to detail ensures a very close reproduction of the full harmonic spectrum of
your guitar’s pickups, resulting in a pure, natural sound that will turn heads at any venue
and/or that records superbly.
The Pre-amplifier
The Plexi 45/50 is designed to be simple in use, and yet produce the quality of sounds that
the musician of today expects from a professional amplifier.
There are two independent channels, each having its own volume control which controls
the overall loudness of the amplifier. The tone controls are designed to work over the
entire frequency range of your guitar, allowing increased amounts of low and high
frequency adjustment.
Channel two has a brighter tone of that of channel one.
The Output Stage
The Plexi 45/50 is a Class ‘AB’ output design and is achieved by means of a negative
voltage applied to the grid of the output valves,
Cathode bias resistors are also employed to stabilise current flow throughout the lifetime of
the valve. The voltage across each resistor will vary with the valve characteristics. When
these voltages are equal, then each valve is drawing the same amount of current and the
valve set is ‘matched’, resulting in maximum output and long life.
